S. H. Yeong

Defect engineering by surface chemical state in boron-doped preamorphized silicon

The continual downscaling of silicon devices for integrated circuits requires the formation of pn junctions that are progressively shallower, incorporate increasing levels of electrically active dopant, and sustain minimal implantation damage. In the case of boron implanted into preamorphized Si, the authors show that all these goals can be accomplished simultaneously through the use of an atomically clean surface, which during annealing acts as a large sink that removes Si interstitials selectively over dopant interstitials.

Understanding of Carbon/Fluorine Co-implant Effect on Boron-Doped Junction Formed during Soak Annealing

The formation of highly activated ultrashallow junctions is one of the main challenges for the forthcoming generation of complementary metal oxide semiconductor (CMOS) devices. Co-implantation of impurities such as carbon (C) or fluorine (F) is an attractive technique. However, junction optimization can only be achieved with a complete understanding of the underlying physical mechanisms. In this paper, the effect of C/F co-implant on boron (B)-doped preamorphized silicon during the soak annealing is extensively studied. C/F atoms are located in the middle range between the B/BF 2 concentration profiles and the end-of-range (EOR) defect band, with the aim of reducing the interactions of dopants with the interstitials released from EOR region. Isochronal annealing study is performed to investigate the impact of C/F codoping on the dopant de/reactivation behavior. It is shown that transient enhanced diffusion can be reduced by both co-implant schemes. The B-doped junction formed with the C co-implant is relatively stable and dopant deactivation is inhibited, while it is presumed that F atoms form B-F complexes, which reduces the B activation level. A physical insight on the dopant-defect interactions associated with C/F co-implant is established through the combination of diffusion and activation studies during soak annealing.

Understanding of Boron Junction Stability in Preamorphized Silicon after Optimized Flash Annealing

Recent research in ultrashallow junction formation has been greatly focused on the development of various advanced annealing techniques. Flash annealing has become one of the most likely candidates to achieve the stringent junction requirements for the forthcoming generation of complementary metal oxide semiconductor devices. In this paper, we present an extensive study on the stability of highly active and ultrashallow B junction in preamorphized silicon formed by optimized flash annealing. Our results demonstrate a strong improvement in junction stability by using the multiple-pulse and pre-spike rapid thermal anneal flash annealing schemes. The deactivation of the flash-annealed junction is clearly shown to be correlated to the different levels of self-interstitial supersaturation, resulting from the release of excess silicon interstitials from the end-of-range defects. We show that optimized multipulse flash annealing could minimize the interaction between point defects and dopant atoms, enabling improvement in junction properties.

Vacancy engineering by optimized laser irradiation in boron-implanted, preamorphized silicon substrate

In this letter, the effect of vacancies generated by preirradiated laser on dopant diffusion and activation in preamorphized silicon substrate has been studied. Laser-induced melting in silicon was used to generate excess vacancies near the maximum melt depth before silicon substrate amorphization and subsequent boron implantation. We demonstrate that by matching the preirradiated laser melt depth with the implant amorphize depth, it can effectively reduce the silicon self-interstitials released from the end-of-range defect band. The results show great suppression in boron transient enhanced diffusion and significant removal of end-of-range defects. This is attributed to the recombination of laser-generated excess vacancies with preamorphizing induced free silicon interstitials at the end-of-range region.

Phosphorus Implant For S/D Extension Formation: Diffusion And Activation Study After Spacer And Spike Anneal

Formation of highly activated S/D extension is one of the key issues to meet the requirements for further downscaling of CMOS devices. Germanium‐preamorphization implant (Ge‐PAI) followed by solid phase epitaxial regrowth (SPER) is capable of forming abrupt and shallow junctions with activation levels well above solid solubility. In this paper, we demonstrate a possible alternative by using phosphorus (P) with the Ge‐PAI and boron (B) Halo implant to form the S/D extension of NMOS. The anomalous diffusion and activation of P after the conventional spacer and spike anneals were studied. We observed that a highly activated and shallow junction can be formed via Ge‐PAI after spacer anneal which is equivalent to a low temperature SPER. The level of P activation is enhanced even more when B Halo is considered. It is postulated that this is due to the competing interactions of B and P with the emitted interstitials of the end‐of‐range (EOR) defects. However, improvement in junction depth and electrical properti...

An Extensive Study on the Boron Junctions Formed by Optimized Pre‐Spike/Multiple‐Pulse Flash Lamp Annealing Schemes: Junction Formation, Stability and Leakage

In this work, the electrical activation of Boron in Germanium pre‐amorphized silicon substrate upon flash lamp annealing (FLA) is investigated. We demonstrate that FLA helps in the reduction of the EOR defects, resulting in minimal transient enhanced diffusion and dopant deactivation effect. It has also been observed that the junction stability improves with the increasing number of flash pulses, which is clearly reflected by the dopant deactivation level upon post‐thermal treatment. In another FLA scheme, the spike rapid thermal annealing (RTA) performed prior to the flash further enhances the junction stability. However, this pre‐spike RTA step induces extensive dopant diffusion and an overall degradation in sheet resistance. The above observations are concluded to be due to the different extent of silicon interstitial supersaturation that can be explained by the interactions between the extended defects and dopants. Lastly, leakage current for the junctions formed under different FLA schemes are compar...

Defect Engineering for Ultra‐Shallow Junctions Using Surfaces

Formation of extremely shallow pn junctions with very low electrical resistance is a maj or stumbling block to the continued down scaling of microelectronic devices. Recent work in our laboratory has shown that the behavior of defects within silicon (and therefore dopants) can be changed significantly by controlling the chemical state of the surface. Certain chemical treatments of the surface induce it to act as an active “sink” for point defects that removes diffusing Si interstitials selectively over impurity interstitials, leading to less dopant diffusion and better electrical activation. The present work demonstrates such effects experimentally for dopants such as boron and arsenic in both crystalline and Ge pre‐amorphized silicon wafers. Surface‐based defect engineering was studied by annealing implanted Si according to various protocols with varying degrees of surface activity toward point defects. After implantation, specimens were heated to stimulate diffusive spreading of the implanted profile, w...

The Impact of Boron Halo on Phosphorus Junction Formation and Stability

In this paper we study the diffusion and activation behaviors of ultrashallow and high concentration of phosphorus (P) dopants in silicon processed with low-temperature thermal annealing. For the first time, significant improvement in dopant activation is observed when a boron halo implant is incorporated in the germanium preamorphized P junction. Our results are discussed in terms of the interactions between dopants and the point defects upon annealing. In addition, no rapid deactivation behavior is observed for the P-doped junction during the isochronal annealing cycle.